Wesley's Blog: What is radiational cooling?

SOUTH MISSISSIPPI (WLOX) -
Along the Gulf Coast, temperatures have been quite cool during recent morning hours. Saturday morning was especially chilly, as expected, with several locations' temperatures dropping into the upper 40s. What gives? It's a meteorological process called "radiational cooling." Here's an explanation:

To begin to understand radiational cooling, you must first recall that Earth has a hot molten core that is releasing heat through the earth's surface all the time. That's called geothermal heat. During the daytime, this geothermal heat is barely noticeable compared to the amount of heat that is pummeling the planet from the sun. But, at night time, geothermal heat helps to keep the earth's surface (a.k.a. the ground, where us human folk live and prosper) from becoming uninhabitably cold.

Think about this heat being released, or radiated, from the ground like your own body which releases small amounts of heat from its skin. At night, when you sleep in bed, you likely throw on a blanket to keep yourself warm. That blanket traps your body's heat right next to you instead of your heat escaping and dispersing into the room.

Well, for Earth, a blanket of clouds at nighttime can accomplish the same heat trapping process. But, on nights with calm winds without any clouds, Earth's geothermal heat radiates from the ground and disperses into the atmosphere... leaving us land-dwellers quite chilly. That's radiational cooling. And it allows temperatures to fall rather quickly during nighttime hours.

High pressure systems generally promote radiational cooling since there are typically clear skies and nearly calm winds around their centers.

Even though high pressure should stick around the Southeast for the next several days, the winds will become too high in south Mississippi for this radiational cooling process to work. Any extra wind on Saturday night will mix the air in the atmosphere up, potentially mixing any dispersed geothermal heat right back down to the ground. Add to that the fact that our winds will be southerly all next week; we'll be tapping into warm and moist air off the Gulf, the added moisture helping to trap nighttime heat and bring an end to south Mississippi's chilly mornings, for now.